This invention relates to an apparatus and method for ex situ vacuum extraction of soils contaminated with volatile and semi-volatile chemical compounds.
There are a large number of sites in the United States and around the world at which soils have been contaminated with volatile and semi-volatile chemical compounds. These contaminants pose significant environmental and human health risks via various routes of exposure, including direct contact, infiltration to soil and ground water, surface water, and air emissions.
These contaminated soils may either be still in the ground where the contamination occurred or already removed and placed in stockpiles. Typically, the stockpiled materials remain at these sites for extended periods of time awaiting proper management, often out of compliance with local, state, and federal regulations. These stockpiles are generally uncontrolled and exposed to the environment, presenting a potential source of contamination via the migration pathways described above. Transportation and disposal of these contaminated soils is very expensive. Under present environmental regulations, depending upon the method of disposal, the original owner may be liable for the soil until it is pronounced environmentally safe. This is known as "cradle to grave" responsibility. The primary method of disposal continues to be placing the contaminated soils in secure landfills. These landfills are filling up at alarming rates. Many landfills are no longer accepting the large quantities of contaminated soil.
Various remediation methods have been developed to address the problem. These methods include incineration of the contaminated soil which is not acceptable in many states, in situ bioremediation, in situ air stripping, in situ flushing and soil washing, vitrification, and solidification/stabilization. Those methods that do not treat the soil but merely relocate them or contain them are becoming less popular.
Vacuum extraction and bioremediation have been used for many years to remediate contaminated soil and ground water. Most of these methods have been in situ, that is leaving the contaminated soil in place and treating the soil with various devices and methods. Ex situ methods such as farming and soil cells can be very costly, specifically due to the transportation costs. These methods lend themselves only to large facilities and sites where the volumes are in excess of five thousands cubic yards. The expense involved is too great to make it financially feasible to use those methods of treatment for small sites, such as gasoline service stations. The apparatus and method described in U.S. Pat. No. 4,919,570 to Fredrick, C. Payne describes a portable on-site soil treatment system. The Payne system describes a system of twelve circular tanks into which the contaminated soil is placed. Conduit connects the tanks in a closed recirculation system with a pump and an activated carbon adsorption system. The entire system remains on flatbed trailers on-site during the treatment of the soil and requires a relatively large continuous area for side by side placement of the trailers and the various elements of the system. Such an area is typically not available on small sites. The Payne device and method requires a major labor expense associated with the setting up of the manifold piping and running it to a separate pumping station as well as the substantial labor cost of breaking down the system at the end of the operation. The soil unloading procedure of the Payne kettles requires a crane to lift the vessels from the trailers for dumping, thus injecting substantial expense, safety concerns, and a requirement of overhead clearance, which is not always available. Further, the Payne device is a substantial installation and would likely create substantial public concern and worry, well beyond the relatively minor environmental problem.
There is a tremendous need for a system and method that will practically and cost effectively decontaminate soils on small sites with volumes of contaminated soils less then one thousand cubic yards. None of the prior devices and methods satisfy these needs nor attain the objects described hereinbelow.